There has been substantial interest in the preparation and characterization of compound semiconductors consisting of particles with dimensions in the order of 2-100 nm, often referred to as quantum dots (QDs) and/or nanoparticles. These studies have focused mainly on the size-tunable electronic, optical and chemical properties of nanoparticles. Semiconductor nanoparticles are gaining substantial interest due to their applicability for commercial applications as diverse as biological labeling, solar cells, catalysis, biological imaging, and light-emitting diodes.
A particularly attractive potential field of application for semiconductor nanoparticle is in the development of next generation light-emitting diodes (LEDs). LEDs are becoming increasingly important, in for example, automobile lighting, traffic signals, general lighting, and liquid crystal display (LCD) backlighting and display screens. Nanoparticle-based light-emitting devices have been made by embedding semiconductor nanoparticles in an optically clear (or sufficiently transparent) LED encapsulation medium, typically a silicone or an acrylate, which is then placed on top of a solid-state LED. The nanoparticles, excited by the primary light of the solid-state LED, emit secondary light, the color of which is characteristic of the particular type and size of the nanoparticles. For example, if the primary emission of the solid-state LED is blue and the characteristic emission of the particular nanoparticle is red, then the nanoparticles will absorb a portion of the blue light and emit red light. A portion of the solid-state LED emission is thereby “down-converted” and the device provides light that is a mixture of blue and red.
The use of semiconductor nanoparticles potentially has significant advantages over the use of the more conventional phosphors. For example, semiconductor nanoparticles provide the ability to tune the emission wavelength of a LED. However even after the nanoparticles have been incorporated into the LED encapsulant, oxygen can still migrate through the encapsulant to the surfaces of the nanoparticles, which can lead to photo-oxidation and, as a result, a drop in quantum yield (QY).
In view of the significant potential for the application of quantum dots across such a wide range of applications, including but not limited to, quantum dot-based light-emitting devices, there is a strong need to develop methods to increase the stability of quantum dots so as to make them brighter, more long-lived and/or less sensitive to various types of processing conditions. There remain significant challenges to the development of quantum dot-based materials and methods for fabricating quantum dot-based devices, such as light-emitting devices, on an economically viable scale and which would provide sufficiently high levels of performance to satisfy consumer demand.